Sucrose, C12H22O11, a disaccharide, is a condensation molecule that links one glucose monosaccharide and one fructose monosaccharide. Sucrose occurs naturally in many fruits and vegetables of the plant kingdom, such as sugarcane, sugar beets, sweet sorghum, sugar palms, or sugar maples. The amount of sucrose produced by plants can be dependent on the genetic strain, soil or fertilization factors, weather conditions during growth, incidence of plant disease, degree of maturity or the treatment between harvesting and processing, among many factors.
Sucrose may be concentrated in certain portions of the plant, for example, the stalks of the sugarcane plant or the sugar beet root. The entire plant, or a portion of the plant in which the sucrose is concentrated, may be harvested and the plant juices may be removed or extracted to obtain a juice containing a certain concentration of sucrose. Typically, the removal or extraction of juices from plant material involves milling, diffusion, pressing, or a combination thereof. Milling is one of the conventional methods for extracting juice from sugar cane stalks. The sugar cane stalks may be cut up into pieces having the desired size and then passed through rollers to squeeze out the juices. This process may be repeated several times down a series of mills to ensure that substantially all the sugar cane juice is removed.
Diffusion is considered to be the conventional method for extracting juice from the root of the sugar beet. Sugar beets may be sliced into thin strips called “cossettes” that may then be introduced into one end of a diffuser while a diffusion liquid, such as warm water, enters the other. When such counter current processing is used about 98 percent of the sucrose from the cossette or sugar beet material can be removed. The resulting sucrose containing liquid is often called “diffusion juice.” The cossettes or beet slices from the diffuser can still be very wet and the juice, which can be 88–92% water, associated with them can still hold some sucrose. The cossettes or beet slices may, therefore, be pressed in a screw press, or other type of press, to squeeze as much juice out of them as possible. This juice often referred to as “pulp press water” can have a pH value of about 5 and in some cases is returned to the diffuser. The resulting pulp may contain about 75% moisture. The addition to the press feed of cationic charged pressing aids can lower the pulp moisture content by about 1.5 to 2%. Sucrose from sugarcane stalks can also be removed by diffusion. One diffusion process for sugarcane involves a moving bed of finely prepared sugarcane pieces passed through the diffuser allowing the sucrose to be leached out of the sugarcane.
The diffusion process, the milling process, other processes that remove juice from plant material, or bring plant juice into aqueous solution, result in a juice containing sucrose, non-sucrose substances, and water. The nature and amount of the non-sucrose substances in the juice obtained by these processes can vary and may include all manner of plant derived substances and non-plant derived substances, including but not limited to: insoluble material, such as, plant fiber or soil particles; and soluble materials, such as, fertilizer, sucrose, saccharides other than sucrose, organic and inorganic non-sugars, organic acids, dissolved gases, proteins, inorganic acids, organic acids, phosphates, metal ions (for example, iron, aluminum, or magnesium ions), pectins, colored materials, saponins, waxes, fats, or gums, their associated or linked moieties, or derivatives thereof.
These non-sucrose substances are often highly colorized, thermally unstable, or otherwise interfere with certain processing steps or adversely impact the quality or quantity of the sugar product resulting from the purification process. It has been estimated that on average one pound of non-sucrose substances reduces the quantity of sugar product resulting from the purification process by one and one-half pounds. It may be desirable to have all or a portion of these non-sucrose substances separated from or removed from the juice resulting from the diffusion, milling, or other methods used to remove juice from the plant material. A good diffusion operation can eliminate 25–30% of entering impurities. Returned pulp or carbonation press water can reduce this level to 17–20%, however it is still economical due to: heat recovery, make up water saved, wastewater pollution reduced, sugar recovered.
Conventional process systems utilize the remaining plant material, or the juice(s) resulting from the diffusion, milling, or other methods used to remove juice from the plant material, such as those described by U.S. Pat. Nos. 6,051,075; 5,928,42; 5,480,490, each hereby incorporated by reference, or such as those described by “Sugar Technology, Beet and Cane Sugar Manufacture” by P. W. van der Poel et al. (1998); “Beet-Sugar Technology” edited by R. A. McGinnis, Third Edition (1982); or Cane Sugar Handbook: A Manual for Cane Sugar Manufacturers and Their Chemists by James C. P. Chen, Chung Chi Chou, 12th Edition (1993), each hereby incorporated by reference herein, to generate various types of: process juices; solids prepared from the remaining plant material or separated from such process juices during their clarification, purification or refining; sugar or sucrose containing juices; sugar or sucrose crystallized from such sugar or sucrose containing juices; mother liquors of such crystallization of sugar or sucrose, along with the various combinations, permutations, by products, or derivative products thereof, each having a level of impurities consistent with the process steps described herein or any portion thereof, or actually utilized in their production, or consistent with conventional standards for a type or kind of product including, but not limited to: animal feeds containing plant material from which juice has been removed such as exhausted beet cossettes, pulp, bagasse, or other solids or juices separated from process juices; power generated using plant material from which juice has been removed as a fuel to boil water to generate high pressure steam to drive turbine(s) in order to make electricity, or to generate low pressure steam for the process system, or to generate low grade heat; syrup ranging from pure sucrose solutions such as those sold to industrial users to treated syrups incorporating flavors and colors, or those incorporating some invert sugar to prevent crystallization of sucrose, for example, golden syrup; molasses obtained by removal of all or any part of the crystallizable sucrose or sugar, or products derived from molasses, one example being treacle; alcohol distilled from molasses; blanco directo or plantation sugars generated by sulfitation using sulfur dioxide (SO2) as a bleaching agent; juggeri or gur generated by boiling sucrose or sugar containing juices until essentially dry; juice sugar from melting refined white sugar or from syrup(s) which may be further decolorized; single-crystallization cane sugars often referred to as “unrefined sugar” in the United Kingdom or other parts of Europe, or referred to as “evaporated cane juice” in the North American natural foods industry to describe a free-flowing, single-crystallization cane sugar that is produced with a minimal degree of processing; milled cane; demerara; muscovado; rapedura; panela; turbina; raw sugar which can be 94–98 percent sucrose, the balance being molasses, ash, and other trace elements; refined sugars such as extra fine granulated having a quality based upon “bottlers” quality specified by the National Soft Drink Association being water white and at least 99.9 percent sucrose; specialty white sugars, such as, caster sugar, icing sugar, sugar cubes, or preserving sugar; brown sugars that can be manufactured by spraying and blending white refined sugar with molasses which can be light or dark brown sugar depending on the characteristics of the molasses; or powdered sugar made in various degrees of fineness by pulverizing granulated sugar in a powder mill and which may further contain corn starch or other chemicals to prevent caking. This list is not meant to be limiting with respect to the products generated from conventional sugar process systems, but rather, it is meant to provide a few examples of the enormous variety of sugar process system products that are generated.
As can be understood, conventional process systems, in part, comprise steps that increasingly clarify, purify, or refine juice(s) resulting from the diffusion, milling, or other methods used to remove juice from the plant material. Typically, a portion of the insoluble or suspended material in sucrose containing juice derived from plant material can be removed using one or more mechanical processes such as screening. The resulting screened juice, when derived from sugar beets, for example, may contain about 82%–85% by weight water, about 13–15% by weight sucrose, about 2.0–3.0% by weight dissolved non-sucrose substances or impurities, and some amount of remaining insoluble materials.
Typically, the resulting sucrose containing juice or juices, which can have a volume of 1000–2500 gallons per minute, may be treated by the gradual addition of base to increase the pH of the juice. In certain conventional process systems, the pH of the juice may be raised from between about 5.5 pH to about 6.5 pH up to between about 11.5 pH to about 11.8 pH to enable certain non-sucrose substances contained in such juices to reach their respective iso-electric points. This step is often referred to as “preliming”. However, the subsequent use of this term is not meant to limit the step of adding base to sucrose containing juice or juices solely to those process systems that refer to this addition of base as “preliming”. Rather it should be understood that in the various conventional juice process systems it may be desirable to first utilize base to raise pH of juice prior to a subsequent process step, such as a filtration step, as described by U.S. Pat. Nos. 4,432,806, 5,759,283, or the like; an ion exchange step as described in British Patent No. 1,043,102, or U.S. Pat. Nos. 3,618,589, 3,785,863, 4,140,541, or 4,331,483, 5,466,294, or the like; a chromatography step as described by U.S. Pat. Nos. 5,466,294, 4,312,678, 2,985,589, 4,182,633, 4,412,866, or 5,102,553, or the like; or an ultrafilitration step as described by U.S. Pat. No. 4,432,806, or the like; phase separation as described by U.S. Pat. No. 6,051,075, or the like; process systems that add active materials to the final carbonation vessel as described by U.S. Pat. No. 4,045,242, that may be an alternative to the conventional juice process steps of main liming and carbonation, each reference hereby incorporated by reference herein.
The use of the term “base” involves the use materials that are capable of increasing the pH of a juice including, but not limited to the use of lime or the underflow from processes that utilize lime. The use of the term “lime” typically involves the specific use of quick lime or calcium oxides formed by heating calcium (generally in the form of limestone) in oxygen to form calcium oxide. Milk of lime is preferred in many juice process systems, and consists of a suspension of calcium hydroxide (Ca(OH)2) in accordance with the following reaction:CaO+H2O⇄Ca(OH)2+15.5 Cal.
The term “iso-electric point” involves the pH at which dissolved or colloidal materials, such as proteins, within the juice have a zero electrical potential. When such dissolved or colloidal materials reach their designated iso-electric points, they may form a plurality of solid particles, flocculate, or flocs.
Flocculation may be further enhanced by the addition of calcium carbonate materials to juice, which functionally form a core or substrate with which the solid particles or flocculates associate. This process increases the size, weight or density of the particles, thereby facilitating the filtration or settling of such solid particles or materials and their removal from the juice.
The resulting mixture of juice, residual lime, excess calcium carbonate, solid particles, flocculants, or flocs, may then be subjected to subsequent process steps as described above. Specifically, with regard to the process system for the clarification, purification, or refining of juices generated by the prior processing of sugar beets, the mixture may first be subjected to a cold main liming step to stabilize the solids formed in the preliming step. The cold main liming step may involve the addition of about another 0.3–0.7% lime by weight of prelimed juice (or more depending on the quality of the prelimed juice) undertaken at a temperature of between about 30 degrees Centigrade to about 40 degrees Centigrade.
The cold main limed juice may then be hot main limed to further degrade invert sugar and other components that are not stable to this step. Hot main liming may involve the further addition of lime to cause the pH of the limed juice to increase to a level of between about 12 pH to about 12.5 pH. This results in a portion of the soluble non-sucrose materials that were not affected by preceding addition of base or lime to decompose. In particular, hot main liming of the limed juice may achieve thermostability by partial decomposition of invert sugar, amino acids, amides, and other dissolved non-sucrose materials.
After cold or hot main liming, the main limed juice can be subjected to a first carbonation step in which carbon dioxide gas can be combined with the main limed juice. The carbon dioxide: gas reacts with residual lime in the main limed juice to produce calcium carbonate in the form of precipitate. Not only may residual lime be removed by this procedure (typically about 95% by weight of the residual lime), but also the surface-active calcium carbonate precipitate may trap substantial amounts of remaining dissolved non-sucrose substances. Furthermore, the calcium carbonate precipitate may function as a filter aid in the physical removal of solid materials from the main limed and carbonated juice.
The clarified juice product obtained from the first carbonation step may then be subjected to additional liming steps, heating steps, carbonation steps, filtering steps, membrane ultrafiltration steps, chromatography separation steps, or ion exchange steps as above described, or combinations, permutations, or derivations thereof, to further clarify or purify the juice obtained from the first carbonation step resulting in a process juice often referred to as “thin juice”.
This further clarified juice or “thin juice” may be thickened by evaporation of a portion of the water content to yield a product conventionally referred to as “syrup”. Evaporation of a portion of the water content may be performed in a multi-stage evaporator. This technique is used because it is an efficient way of using steam and it can also create another, lower grade, steam which can be used to drive the subsequent crystallization process, if desired.
The thickened clarified juice or “syrup” can be placed into a container, which may typically hold 60 tons or more. In the container, even more water is boiled off until conditions are right for sucrose or sugar crystals to grow. Because it may be difficult to get the sucrose or sugar crystals to grow well, some seed crystals of sucrose or sugar are added to initiate crystal formation. Once the crystals have grown the resulting mixture of crystals and remaining juice can be separated. Conventionally, centrifuges are used to separate the two. The separated sucrose or sugar crystals are then dried to a desired moisture content before being packed, stored, transported, or further refined, or the like. For example, raw sugar may be refined only after shipment to the country where it will be used.
There is a competitive global commercial market for the products derived from sucrose containing plant materials and juices. The market for products produced from sucrose containing plant material has sufficient size that even a slight reduction in the cost of a single process system step can yield a substantial and desired monetary savings. As such, there is great incentive to perform research in sugar or juice process systems by the sugar industry to yield process system savings, by independent researchers and by distributors who may be paid for novel process system chemicals and equipment, and in some cases have a further incentive by additional payments based upon a percentage of the savings within the process when improvements are made.
However, even though process systems for the purification of sucrose containing juices from certain plant materials have been established and improved upon for at least 1000 years, and specifically with regard to sugar beets, there have been commercial process systems for more than 100 years, and even though there is great incentive to generate improvements within sugar or juice process systems, significant problems with regard to the processing of juices obtained from plant material remain.
A significant problem with conventional sugar processing systems can be the expense of obtaining and using base, such as calcium oxide, to raise the pH of the sucrose containing liquids or juice(s) obtained from plant materials. As discussed above, calcium oxide or calcium hydroxide may be added to juice to raise the pH allowing certain dissolved materials to come out of solution as solids, flocculent, or flocs. Calcium oxide is typically obtained through calcination of limestone a process in which the limestone is heated in a kiln in the presence of oxygen until carbon dioxide is released resulting in calcium oxide.
As shown by FIG. 5, calcination can be expensive because it requires the purchase of the kiln (40), limestone (41), and fuel (42), such as gas, oil, coal, coke, or the like, that can be combusted to raise the temperature of the kiln sufficiently to release carbon dioxide (43) from the limestone (41). Ancillary equipment to transport the limestone and the fuel to the kiln and to remove the resulting calcium oxide from the kiln must also be provided along with equipment to scrub certain kiln gases and particles from the kiln air exhausted during calcination of the limestone. Naturally, labor must be provided to operate and maintain the equipment, as well as, monitor the quality of the calcined limestone generated and also to monitor the clean up of gases and particulates released during operation of the kiln.
Additionally, the calcium oxide generated by calcination must be converted to calcium hydroxide for use in typical juice process systems. Again this involves the purchase of equipment to reduce the calcium oxide to suitably sized particles and to mix these particles with water to generate calcium hydroxide. Again, labor must be provided to operate and  maintain this equipment.
Finally, the investment in equipment and labor associated with the use of calcium oxides incrementally increases as the amount used increases. This may involve the incremental expenditure for the additional labor to mix additional amounts of calcium hydroxide with juice, or it may involve an incremental expenditure to use equipment having greater loading capacity or having greater power, or the like.
Another significant and related problem with the production of and use of base in conventional process systems can be disposal of excess base or the products formed when the base reacts with organic acids or inorganic acids dissolved in the juice. For example, when the process system uses one or more carbonation steps in clarifying or purifying juice, the amount of calcium carbonate or other salts formed, often referred to as “spent lime”, will be proportionate to the amount of lime added to the juice. Simply put, the greater the amount of lime added to the juice, generally the greater the amount of precipitates formed during the carbonation step The “carbonation lime” may be allowed to settle to the bottom of the carbonation vessel forming what is sometimes referred to as a “lime mud”. The lime mud can be separated by a rotary vacuum filter or plate and frame press. The product formed is then called “lime cake”. The lime cake or lime mud may largely be calcium carbonate precipitate but may also contain sugars, other organic or inorganic matter, or water. These separated precipitates are almost always handled separately from other process system wastes and may, for example, be slurried with water and pumped to settling ponds or areas surrounded by levees or transported to land fills.
Alternately, the carbonation lime, lime mud, or lime cake can be recalcined. However, the cost of a recalcining kiln and the peripheral equipment to recalcine spent lime can be substantially more expensive than a kiln for calcining limestone. Furthermore, the quality of recalcined “carbonation lime” can be different than calcined limestone. The purity of calcined limestone compared to recalcined carbonation lime may be, as but one example, 92% compared with 77%. As such, the amount of recalcined lime required to neutralize the same amount of hydronium ion in juice may be correspondingly higher. Also, the carbon dioxide content of spent lime can be much higher than limestone. As such, not only can recalcined lime be expensive to generate, it can also require the use of substantially larger gas conduit and equipment to transfer the generated CO2 from recalcining spent lime, larger conveying equipment to move the recalcined lime, larger carbonation tanks, or the like.
Also whether spent lime is disposed of in ponds, landfills, or by recycling, the greater the amount of lime utilized in a particular process system, generally the greater the expense of disposing the spent lime.
Another significant problem with conventional sugar processing systems may be an incremental decrease in process system throughput corresponding with an incremental increase in the amount of lime used in processing juice(s). One aspect of this problem may be that there is a limit to the amount of or rate at which lime can be produced or provided to juice process steps. As discussed above, lime stone must be calcined to produce calcium oxide prior to its use as a base in juice process systems. The amount of lime produced may be limited in by availability of limestone, kiln capacity, fuel availability, or the like. The rate at which lime can be made available to the juice process system may vary based on the size, kind, or amount of the lime generation equipment, available labor, or the like. Another aspect of this problem can be that the amount of lime used in the process system may proportionately reduce volume available for juice in the process system. Increased use of base, such as lime, may also require the use of larger containment areas, conduits, or the like to maintain throughput of the same volume of juice.
Another significant problem with conventional sugar processing systems may be excess acids within plant material generated prior to extraction of the plant juice. Organic acids act as a buffering system in the acid-base equilibrium of the plant cell, in order to maintain the required pH value in the plant tissue. The origin of these acids can be divided into two groups, the first, are acids taken up by the plant from the soil in the course of the growing cycle, and the second, are acids formed by biochemical or microbial processes. When the uptake of acids from the soil is insufficient, plants may synthesize organic acids, primarily oxalic acid, citric acid and malic acid, to maintain a healthy pH value of the plant cell juice. As such, juice extracted from the plant tissue will contain a certain amount of various organic acids.
In addition to this naturally occurring amount of organic acids within the plant tissue, acids may be formed during storage primarily by microbial processes. Badly deteriorating plant material may generate large amounts of organic acids, primarily lactic, acetic acid, as well as citric acid. The total acid content within the plant tissue can increase threefold, or more, under certain circumstances.
Moreover, carbon dioxide (CO2) can be generated in the plant tissues due to breakdown of the natural alkalinity in the juice. In this process, bicarbonate ion and carbonate ion are converted to carbon dioxide. The resulting carbon dioxide to the extent it remains in solution generates carbonic acid that provides a source of hydronium ion. Organic acids contained within the plant cell juice, in whole or in part, remain within the juice obtained from the plant material. As such, to raise the pH of the juice, these organic and inorganic acids must be neutralized with base. The higher the concentration of organic acids or inorganic acids within the juice, the greater the amount of base that may be necessary to raise the pH of the juice to a desired value.
Another significant problem with conventional sugar processing systems may be that plant materials or juice(s) treated with antimicrobial chemicals can have higher acid content then untreated plant materials or juices. For example, sulfur dioxide (SO2) or ammonium bisulfite (NH4HSO3) can be added continuously or intermittently to help control microbial growth or infection. The amount of SO2 added depends on the severity of the microbial growth or infection. Lactic acid and nitrite levels can be monitored or tracked to determine severity of growth or infection. Up to about 1000 ppm of SO2 can be used to shock or treat an infected system. Up to 400–500 ppm can be fed continuously to control an infection. The SO2 or NH4HSO3 addition used for antimicrobial protection can lower the pH and alkalinity of juice(s). The alkalinity reduction may occur due to conversion of naturally occurring bicarbonate ions to CO2 and carbonic acid.
Another significant problem with conventional sugar processing systems may be the formation of scale in containment vessels, such as, evaporators or sugar crystallization equipment. The calcium salt of oxalic acid often forms the main component of scale. Oxalate has low solubility in solution and that solubility can be reduced as the amount of calcium in solution increases. Even after juice purification to “thin” or “thick” juices there can be sufficient calcium in solution to force oxalate out of solution. The process of removing scale from the surfaces of equipment can be expensive, including, but not limited to, costs due to production slowdowns and efficiency losses, or the reduction in the effective life of equipment.
Another significant problem with convention sugar processing systems may be the lack of recognition that juice extraction equipment or processes used to obtain juice from plant material can alter or reduce the pH of the extracted juice. With respect to diffusers used to extract juice from sugar beet material, there may have been a failure to recognize that the pH value of sugar beet juice can be altered or reduced during the diffusion process. Another aspect of this-problem may be that there may be a lack of recognition that different apparatus or different methods used to diffuse juice from sugar beet material alters or reduces the pH of the juice obtained differentially. To the extent that improvements in diffusion technology have generally resulted in increasingly lower pH values of the juice obtained, these apparatuses and methods teach away from the solutions provided by the invention.
The present invention provides a juice process system involving both apparatuses and methods that address each of the above-mentioned problems.